I use photobucket.com
You upload pictures to their site and you can hotlink your pictures to this site.
To hotlink you use this format:
[ img ]your picture's web address[ / img ]
Don't use any spaces (I used spaces to show you the format) and you should be good to go!
Using photobucket, they offer links already formatted like I did above. You just click on the [img] link under your uploaded picture and it'll copy to your clipboard. Then just paste it into the message body of your post and you're done.